On Feb 20, 2015, at 1:50 AM, Michael Kerrisk <mtk.manpages@xxxxxxxxx> wrote:
> Hello Ted,
> Based on your commit message 0ae45f63d4e, I I wrote the documentation
> below for MS_LAZYTIME, to go into the mount(2) man page. Could you
> please check it over and let me know if it's accurate. In particular,
> I added pieces marked with "*" below that were not part of the commit
> message and I'd like confirmation that they're accurate.
> MS_LAZYTIME (since Linux 3.20)
> Only update filetimes (atime, mtime, ctime) on the in-
> memory version of the file inode. The on-disk timeâ
> stamps are updated only when:
> (a) the inode needs to be updated for some change unreâ
> lated to file timestamps;
> (b) the application employs fsync(2), syncfs(2), or
> (c) an undeleted inode is evicted from memory; or
> * (d) more than 24 hours have passed since the i-node was
> * written to disk.
> This mount option significantly reduces writes to the
> inode table for workloads that perform frequent random
> writes to preallocated files.
> * As at Linux 3.20, this option is supported only on ext4.
I _think_ that the lazytime mount option is generic for all filesystems.
I believe ext4 has an extra optimization for it, but that's it.